A comparison of sampling and analysis methods for low-ppbC levels of volatile organic compounds in ambient air

A carefully designed study was conducted during the summer of 1998 to collect samples of ambient air by canisters and compare the analysis results to direct sorbent preconcentration results taken at the time of sample collection. Thirty-two 1 h sample sets were taken, each composed of a "near-real-time" sample analyzed by an autoGC-MS XonTech 930/Varian Saturn 2000 system, and Summa and Silco canisters. Hourly total non-methane organic carbon (TNMOC), ozone, and meteorological measurements were also made. Each canister was analyzed on the autoGC-MS system for a target list of 108 volatile organic compounds (VOCs) and on a manual cryosampling GC-FID system. Comparisons were made between the collection and analysis methods. Because of the low sample loading (150-250 ppbC TNMOC), these comparisons were a stringent test of sample collection and analysis capabilities. The following specific conclusions may be drawn from this study. Reasonable precision (within 15% mean difference of duplicate analyses from the same canister) can be obtained for analyses of target VOCs at low-ppbC concentrations. Relative accuracy between the GC-MS and GC-FID analysis methods is excellent, as demonstrated by comparisons of analyses of the same canisters, if measurements are sufficiently above the detection limits. This is especially significant as the GC-MS and GC-FID were independently calibrated. While statistically significant differences may be observed between the results from canister and near-real-time samples, the differences were generally small and there were clear correlations between the canister results and the near-real-time results. Canister cleanliness limits detection below the EPA Method TO-14 acceptance standard of 0.2 ppbv (0.2-2 ppbC for target analytes).     

Agro-predation: usurpation of attine fungus gardens by Megalomyrmex ants

 A new ant species of Megalomyrmex conducts mass raids to usurp gardens of the fungus-growing ant Cyphomyrmex longiscapus, then lives in the gardens and consumes the cultivated fungus. Unlike attine ants, however, Megalomyrmex sp. does not forage for substrate to manure the gardens; therefore, when gardens become depleted, Megalomyrmex sp. must locate and usurp new gardens. Megalomyrmex sp. workers feed their larvae with attine brood, but only after removing the fungal mycelium that covers the attine larval integument, suggesting that this fungal coat may provide partial protection against other predators. Unlike other known Megalomyrmex species, which coexist as social parasites in attine colonies, Megalomyrmex sp. expels its attine hosts during the garden raids. Megalomyrmex sp. thus maintains a unique agro-predatory lifestyle that is described here for the first time. Received: 18 August 2000 / Accepted in revised form: 1 November 2000     

Biogeography of bacterioplankton in lakes and streams of an Arctic tundra catchment

Bacterioplankton community composition was compared across 10 lakes and 14 streams within the catchment of Toolik Lake, a tundra lake in Arctic Alaska, during seven surveys conducted over three years using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified rDNA. Bacterioplankton communities in streams draining tundra were very different than those in streams draining lakes. Communities in streams draining lakes were similar to communities in lakes. In a connected series of lakes and streams, the stream communities changed with distance from the upstream lake and with changes in water chemistry, suggesting inoculation and dilution with bacteria from soil waters or hyporheic zones. In the same system, lakes shared similar bacterioplankton communities (78% similar) that shifted gradually down the catchment. In contrast, unconnected lakes contained somewhat different communities (67% similar). We found evidence that dispersal influences bacterioplankton communities via advection and dilution (mass effects) in streams, and via inoculation and subsequent growth in lakes. The spatial pattern of bacterioplankton community composition was strongly influenced by interactions among soil water, stream, and lake environments. Our results reveal large differences in lake-specific and stream-specific bacterial community composition over restricted spatial scales (<10 km) and suggest that geographic distance and connectivity influence the distribution of bacterioplankton communities across a landscape.     

Organization of Plethodon salamander communities: guild-based community assembly

A long-standing goal in evolutionary ecology is to determine whether the organization of communities is reflective of underlying deterministic processes. In this study, I examined patterns of species co-occurrence among eastern Plethodon salamanders and determined whether they were consistent with predictions from a guild model of competition-based community assembly. Using a database of 45 species and 4540 geographic sites, I found that patterns of co-occurrence were significantly nonrandom at both a regional and continental scale, and species of different size guilds were distributed more evenly in sites than was expected by chance. Sites with the highest species richness had consistent patterns of community composition, and with few exceptions, the same five species were present at all sites. Taken together, these results imply that larger Plethodon communities are assembled from simpler communities in a manner consistent with what is predicted through competitive mechanisms and suggest that stable species combinations are possible to achieve at various levels of species richness. These results also provide strong evidence consistent with the hypothesis that competitive-based community assembly is a general phenomenon in Plethodon and that interspecific competition is prevalent among the eastern species of this group.     

State-of-the-science assessment of non-asbestos amphibole exposure: Is there a cancer risk?

The distinction between amphibole asbestos fibers and non-asbestos amphibole particles has important implications for assessing potential cancer risks associated with exposure to amphibole asbestos or amphibole-containing products. Exposure to amphibole asbestos fibers can pose a cancer risk due to its ability to reside for long periods of time in the deep lung (i.e., biopersistence). In contrast, non-asbestos amphibole particles are usually cleared rapidly from the lung and do not pose similar respiratory risks even at high doses. Most regulatory and public health agencies, as well as scientific bodies, agree that non-asbestos amphiboles possess reduced biological (e.g., carcinogenic) activity. Although non-asbestos amphibole minerals have been excluded historically from Federal regulations, non-asbestos structures may be counted as asbestos fibers on the basis of dimensional criteria specified in analytical protocols. Given the potential to mischaracterize a non-asbestos structure as a “true” asbestos fiber, our objective was to assess whether exposure to non-asbestos amphiboles that may meet the dimensional criteria for counting as a fiber pose a cancer risk similar to amphibole asbestos. We reviewed analytical methods as well as the mineralogical, epidemiological, and toxicological literature for non-asbestos amphiboles. No evidence of demonstrable cancer effects from exposure to non-asbestos amphiboles that may be counted as fibers, under certain assessment protocols, was found. Data gaps (industrial hygiene data for amphibole-exposed cohorts), inconsistencies (analytical laboratory methods/protocols used to count fibers), and sources of potential bias from misclassification of exposure were identified.     

Predicting the spatial distribution of mangroves in a South African estuary in response to sea level rise,substrate elevation change and a sea storm event

The spatial distribution of mangroves in the Mngazana Estuary under sea level rise induced by climate change, together with different substrate elevation change scenarios was predicted for 2020, 2050 and 2100. The present inundation frequency tolerance range was from 0.8 to 31.2 %, equivalent to substrate elevation thresholds of 1.1 and 1.7 m amsl. These thresholds were measured by field surveys and analysis of a gauge station situated near the mouth of the estuary. The predictions were based on the assumption that the inundation frequency tolerance range of mangrove stands remains constant in the future. Through the use of a digital elevation model an initial increase of 2.10 ha year^?1 was found in mangrove area between present and 2020 (from 122.6 to 143.6 ha). This was due to habitat becoming available that is currently too compacted for seedling establishment to occur. This compaction resulted from human and cattle traffic for grazing. Thereafter there would be a mean loss of 0.66 ha year^?1 from 2020 through 2100. Landward migration of mangroves would not take place due to the elevation limit of adjacent non-mangrove areas. In addition, the loss rate would increase to 1.01 ha year^?1 under insufficient sediment accretion, but would decrease to 0.18 ha year^?1 under thriving mangroves condition. The analysis of sea storm event in September 2008 showed that local water level increased by 28 cm and maximum affected area was 87.0 ha (about 71 % of mangrove stands). The inundation continued over 5 days. The results indicated that the combination impact of sea level rise, substrate elevation change and sea storm would possibly be a threat to tropical African estuaries with large flat intertidal areas and mangroves.     

An updated assessment of the acute impacts of ocean carbon sequestration by direct injection

This paper evaluates the expected environmental impact of several promising schemes for ocean carbon sequestration by direct injection of CO₂, and serves as a major update to the assessment by Auerbach et al. (1997) and Caulfield et al. (1997) of water quality impacts and the induced mortality to zooplankton. Three discharge approaches are considered, each designed to maximize dilution over the water column: a point release of negatively buoyant CO₂ hydrate particles from a moving ship; a stationary point release of CO₂ hydrate particles forming a sinking plume; and a long, bottom-mounted diffuser discharging buoyant liquid CO₂ droplets. Two of these scenarios take advantage of the enhanced dilution offered by CO₂ hydrate particles, and are based on recent laboratory and field studies on the formation and behavior of such particles. Overall, results suggest that it is possible with present or near present technology to engineer discharge configurations that achieve sufficient dilution to largely avoid acute impacts. In particular, the moving ship hydrate discharge is identified as the most promising due to its operational flexibility. In addition to lethal effects, sub-lethal and ecosystem effects are discussed qualitatively, though not analyzed quantitatively. Our main conclusion is that ocean carbon sequestration by direct injection should not be dismissed as a climate change mitigation strategy on the basis of environmental impact alone. Rather, it can be considered as a viable option for further study, especially in regions where geologic sequestration proves impractical.     

Occurrence and formation of trihalomethanes in marine aquaria studied using solid-phase microextraction gas chromatography-mass spectrometry

The occurrence and formation of chlorinated and brominated trihalomethanes (THMs) were studied in artificial saltwater and natural seawater marine aquaria as well as in groundwater and surface waters. A new headspace solid-phase microextraction method was used, which included gas chromatography-mass spectrometry and provided method detection limits of less than 0.1 microg/L, with a signal-to-noise ratio of 3 to 5. The results showed that disinfection by using either chlorine or ozone caused a significant formation of THMs in situ. Speciation of the THMs was a strong function of the water matrix, with initial bromide concentrations playing a pivotal role. These results provide a tool for understanding and monitoring the formation of key disinfection byproducts in marine aquaria that may cause respiratory, eye irritation, or other health concerns.     

CFD modelling of hydrogen release, dispersion and combustion for automotive scenarios

The paper describes the analysis of the potential effects of releases from compressed gaseous hydrogen systems on commercial vehicles in urban and tunnel environments using computational fluid dynamics (CFD). Comparative releases from compressed natural gas systems are also included in the analysis.

This study is restricted to typical non-articulated single deck city buses. Hydrogen releases are considered from storage systems with nominal working pressures of 20, 35 and 70 MPa, and a comparative natural gas release (20 MPa). The cases investigated are based on the assumptions that either fire causes a release via a thermally activated pressure relief device(s) (PRD) and that the released gas vents without immediately igniting, or that a PRD fails. Various release strategies were taken into account. For each configuration some worst-case scenarios are considered.

By far the most critical case investigated in the urban environment, is a rapid release of the entire hydrogen or natural gas storage system such as the simultaneous opening of all PRDs. If ignition occurs, the effects could be expected to be similar to the 1983 Stockholm hydrogen accident [Venetsanos, A. G., Huld, T., Adams, P., & Bartzis, J. G. (2003). Source, dispersion and combustion modelling of an accidental release of hydrogen in an urban environment. Journal of Hazardous Materials, A105, 1–25]. In the cases where the hydrogen release is restricted, for example, by venting through a single PRD, the effects are relatively minor and localised close to the area of the flammable cloud. With increasing hydrogen storage pressure, the maximum energy available in a flammable cloud after a release increases, as do the predicted overpressures resulting from combustion. Even in the relatively confined environment considered, the effects on the combustion regime are closer to what would be expected in a more open environment, i.e. a slow deflagration should be expected.

Among the cases studied the most severe one was a rapid release of the entire hydrogen (40 kg) or natural gas (168 kg) storage system within the confines of a tunnel. In this case there was minimal difference between a release from a 20 MPa natural gas system or a 20 MPa hydrogen system, however, a similar release from a 35 MPa hydrogen system was significantly more severe and particularly in terms of predicted overpressures. The present study has also highlighted that the ignition point significantly affects the combustion regime in confined environments. The results have indicated that critical cases in tunnels may tend towards a fast deflagration, or where there are turbulence generating features, e.g. multiple obstacles, there is the possibility that the combustion regime could progress to a detonation.

When comparing the urban and tunnel environments, a similar release of hydrogen is significantly more severe in a tunnel, and the energy available in the flammable cloud is greater and remains for a longer period in tunnels. When comparing hydrogen and natural gas releases, for the cases and environments investigated and within the limits of the assumptions, it appears that hydrogen requires different mitigation measures in order that the potential effects are similar to those of natural gas in case of an accident. With respect to a PRD opening strategy, hydrogen storage systems should be designed to avoid simultaneous opening of all PRD, and that for the consequences of the released energy to be mitigated, either the number of PRDs opening should be limited or their vents to atmosphere should be restricted (the latter point would require validation by a comprehensive risk assessment).